linux-kernel - Re: [GIT PATCH] more Driver core patches for 2.6.19

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Message-Id: <1166049549.11914.218.camel@localhost.localdomain>
Date:	Thu, 14 Dec 2006 09:39:08 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	tglx@...utronix.de
Cc:	Linus Torvalds <torvalds@...l.org>, Greg KH <gregkh@...e.de>,
	Andrew Morton <akpm@...l.org>, linux-kernel@...r.kernel.org
Subject: Re: [GIT PATCH] more Driver core patches for 2.6.19

On Wed, 2006-12-13 at 23:30 +0100, Thomas Gleixner wrote:
> On Thu, 2006-12-14 at 09:14 +1100, Benjamin Herrenschmidt wrote:
> > the edge flow is easy. the level one is:
> > 
> >  - IRQ happens
> >  - kernel handler masks it and queue a msg for userland
> >  - later on, userland gets the message, talks to the device,
> >    (MMAP'ed mmio, acks the interrupt on the device itself) and
> >    does an ioctl/syscall/write/whatever to tell kernel it's done
> >  - kernel unmasks it.
> 
> That's simply not true.
> 
> - IRQ happens
> - kernel handler runs and masks the chip irq, which removes the IRQ
> request
> - user space message get queued or waiting reader woken
> - kernel handler returns IRQ_HANDLED, which reenables the irq in the PIC
> - user space handles the device
> - user space reenables the device irq
> 
> No need for an ioctl. Neither for edge nor for level irqs.

Wait wait wait... your scenario implies that the kernel has knowledge of
the chip to mask the irq in the chip in the first place.

If that is the case, then you have a chip specific kernel driver,
yadada, the whole story is moot :-)

We were talking about the idea of having some "generic" reflector of
irqs to userspace without device specific knowledge.

Ben.

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